Altered transcriptional regulation is a major contributor to the neoplastic characteristics of most tumor cells. New technological advances, such as DNA microchips, have allowed investigators to perform large scale comparisons of gene expression differences in normal versus cancer cells. However, there many unanswered questions concerning the transcription factors which are altered in cancers, their target genes, and the mechanisms by which transcriptional regulation is achieved. We have chosen to focus on three families of transcription factors due to extensive evidence linking them to the control of cell proliferation. E217 factors control genes involved in DNA synthesis and cell cycle progression and regulators of this family are mutated in the majority of human tumors. The Myc family has also been implicated in the development of many cancers and Myc factors regulate genes required for DNA and protein synthesis and telomere maintenance. Finally, the TCF family of transcription factors, in cooperation with beta-catenin, is thought to be a major contributor in the development of colon cancer, a leading cause of cancer death in the U.S. In Aim I, we propose to investigate whether current models of transcriptional regulation accu- rately reflect gene expression mediated by these factors. We will do so by determining if all S phase cells display identical gene expression profiles (using in situ hybridizations and reporter assays) and by deter- mining if complexes containing different members of the E2F, Myc, or TCF families are functionally equivalent (using a chromatin immunoprecipitation assay which monitors DNA/protein interactions in living cells). In Aim II, We propose to compare transcriptional regulation by these factors in cell cultures versus human tumors. For these experiments, we have recently demonstrated that our chromatin immunoprecipitation assay can directly monitor transcription factor binding to target promoters in surgical samples. Finally, in Aim III, we propose to modify our chromatin immunoprecipitation assay to identify novel target genes regulated by the E2F, Myc, and TCF factors in normal and cancer cells.